U.S. Pat. No. 4,232,140 discloses a vanadiumcontaining catalyst system for polymerizing ethylene comprising:
(A) a solid catalyst component containing: PA1 (B) an alkylaluminum cocatalyst, and PA1 (C) trichlorofluoromethane. PA1 (A) a solid catalyst component consisting essentially of PA1 (B) an alkylaluminum cocatalyst, and PA1 (C) a halohydrocarbon polymerization promoter. PA1 (A) a solid catalyst component consisting essentially of PA1 (B) an alkylaluminum cocatalyst, and PA1 (C) a halohydrocarbon polymerization promoter, PA1 R and R.sup.1 are alkyl radicals containing from 1 to 14 carbon atoms, which radicals may be the same or different, and PA1 n is an integer having a value of from 1 to 2. PA1 (A) a solid catalyst component consisting essentially of PA1 (B) an alkylaluminum cocatalyst, and PA1 (C) a halohydrocarbon polymerization promoter.
(a) a vanadium chloride, PA2 (b) an alkylaluminum alkoxide, and PA2 (c) an inert inorganic support, PA2 (1) an inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and PA2 (3) a boron halide or alkylaluminum compound, PA2 (1) a solid, particulate, porous inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and PA2 (3) a boron halide or alkylaluminum compound, PA2 (1) a solid, particulate, porous inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, PA2 (3) an alkylaluminum alkoxide molecular weight distribution (MWD) regulator having the formula R.sub.n Al(OR.sup.1).sub.3-n, wherein R, R.sup.1 and n are as defined above,
However, this reference does not disclose use of an electron donor in such catalyst system nor provide means for regulating the molecular weight distribution of the polymers produced with such catalyst system.
U.S. Pat. No. 4,508,842 discloses a highly active vanadium-containing catalyst capable of producing ethylene polymers having a broad molecular weight distribution. Said catalyst comprises:
The polymers produced in accordance with U.S. Pat. No. 4,508,842 have a relatively broad molecular weight distribution, and excellent extrudability. These properties render them extremely useful in a wide variety of applications, such as wire and cable insulation, blow molding, film, and pipe fabrication. However, such polymers cannot be used in other applications, such as injection molding, which require a narrower molecular weight distribution.